A marimba effect is produced by alternately pounding two musical tones of different pitch in a percussive fashion. In an electronic organ or similar keyboard-operated instrument. An electronic organ or similar keyboard-operated instrument, the marimba effect is provided as an accompaniment or background to the music being played. Typically, when a note sounded by depressing a key on the keyboard, in addition to generating a conventional tone associated with that key, two percussive sounds at different frequencies are sounded alternately at a predetermined rate.
The present invention is directed to an electronic circuit for creating the marimba-type effect in a tone synthesizer of the type described in detail in co-pending application U.S. Ser. No. 603,776, filed Aug. 11, 1975, entitled "Polyphonic Tone Synthesizer" now issued as U.S. Pat. No. 4,085,644. The tone generator described in the above-identified application synthesizes a musical sound by computing a master data set, transferring the data set to a buffer memory from which the data is repetitively read out in real time at a rate determined by the pitch of the tone being generated, the data being applied to a digital to-analog converter, which transforms the buffer memory output data to an analog voltage waveform for driving an audio sound system. The master data set is created repetitively and independently of tone generation by computing a Fourier sine equation using stored sets of generalized Fourier coefficients and a table of sinusoid data.
The present invention is directed to improvements in a portion of the tone synthesizer described in the above-identified application to create a modified master data set to include information on the super imposed marimba effect.